Salt-based method to monitor and log the times a data center air goes above a predefined limit

ABSTRACT

A salt-based method to monitor and log the time periods a data center air&#39;s relative humidity goes above a predefined limit. The choice of the salt is such that its deliquescent relative humidity is equal to the desired limit, so that above the desired limit, the salt gets wet and therefore electrically conductive. An alarm can then give notice that relative humidity levels are above acceptable levels so that remedial action may be taken before problems such as electronic malfunction develop.

BACKGROUND

Electronic equipment exposed to high levels of relative humidity insurrounding air may often times corrode. Early mitigation of highrelative humidity conditions may avoid such problems.

SUMMARY

In an embodiment, an apparatus to monitor the relative humidity of airgoing above a predefined value is provided. The apparatus includes:metallic, inter-digitated comb patterns printed on a medium havingspacing in between the patterns wherein a saturated liquid solutioncontaining salt is dried upon the medium, the salt having a deliquescentrelative humidity, wherein the dried salt absorbs moisture and becomesionically conductive when exposed to relative humidity levels exceedingthe salt's deliquescent relative humidity. Also included is a powersupply and a high resistance resistor connected to the inter-digitatedcomb pattern in series and forming an electrical circuit; and amicroprocessor connected across the high resistance resistor whichmonitors changes in resistance of the circuit that result from the saltbecoming ionically conductive thereby indicating an incident of relativehumidity of the air exceeding a predefined value based on the salt'sdeliquescent relative humidity.

In another embodiment, an apparatus to monitor the relative humidity ofair going above a predefined value is provided.

The apparatus includes: a sand blasted printed circuit board comprisingmetallic, inter-digitated comb patterns printed on a medium havingspacing in between the patterns wherein a saturated liquid solutioncontaining salt is dried upon the medium, the salt having a deliquescentrelative humidity, wherein the dried salt absorbs moisture and becomesionically conductive when exposed to relative humidity levels exceedingthe salt's deliquescent relative humidity. Also included is a powersupply and a high resistance resistor connected to the inter-digitatedcomb pattern in series forming an electrical circuit; and amicroprocessor connected across the high resistance resistor whichmonitors changes in resistance of the circuit that result from the saltbecoming ionically conductive thereby indicating an incident of relativehumidity of the air exceeding a predefined value based on the salt'sdeliquescent relative humidity.

In another embodiment, a method to monitor the relative humidity of airexceeding a predefined value is provided. The method includes:

providing metallic inter-digitated comb patterns printed on a mediumhaving spacing in between the patterns; coating the patterns and mediumwith a liquid solution containing salt, the salt having a deliquescentrelative humidity;allowing the solution to dry; connecting, in series, a power supply, ahigh resistance resistor and a microprocessor to the comb patternthereby creating an electrical circuit; connecting at least one of adata logger and an alarm circuit to the microprocessor; monitoring, bythe microprocessor, the resistance of the circuit as a current passesthrough the circuit; and triggering the alarm circuit in response to thecurrent exceeding a threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a platinum inter-digitated comb coupon printed on a 2-mmthick quartz frit disk. The pores in the frit contain sodium nitritesalt.

FIG. 2 describes the circuit used to detect when the relative humidityrises above a predetermined level.

FIG. 3 depicts the process to check for relative humidity exceeding thepreset threshold.

FIG. 4 depicts the process to check for relative humidity exceeding thepreset threshold including use of an air mixer.

DETAILED DESCRIPTION

The industry wide recommended relative humidity limit below whichelectronic hardware is designed to operate reliably is 60%. Relativehumidity in data centers above this limit can cause electroniccomponents to malfunction, potentially resulting in computing disruptionand loss of data.

The present invention relates to a salt-based device and a circuit tomonitor and log the time periods a data center air's relative humiditygoes above a predefined limit so that action may be taken beforeproblems such as electronic malfunction develop. Current techniques ofmeasuring the relative humidity are based on sensor technology that hasan accuracy of ±2% or even more. With the ever increasing use of outsideair for cooling IT equipment, there is a need to monitor the relativehumidity of the air forced into the data center to cool the ITequipment. The need to monitor the air for relative humidity is evenmore relevant on rainy, damp or very humid days when the combination ofmechanical cooling combined with outside air cooling can lead tocondensation and enhanced corrosion. Dew point measurement may providean alternative for data center moisture level monitoring, but the dewpoint is calculated from relative humidity and temperature data. Bothtemperature and relative humidity have a measurement error that ispropagated along the dew point calculation which may lead to inaccuratemeasurements.

Deliquescent relative humidity is the relative humidity above which saltabsorbs water and thus gets wet and ionically conductive. Thedeliquescent relative humidity is solely determined by the chemicalproperties of the salt used for monitoring. As long as the salt remainspure, its deliquescent relative humidity will remain unchanged.

In an embodiment, a very precise relative humidity data logger deviceutilizing salt and based on sodium nitrite chemistry is shown. Thedeliquescent relative humidity of the salt chosen to build the deviceshould be near or equal to the desired relative humidity limit. The saltis dissolved preferably in distilled water to limit impurities tomaintain consistent deliquescent relative humidity.

Sodium nitrite is a good choice for building the device because itsdeliquescent relative humidity is 62% which is quite close to thedesired relative humidity limit of 60%. The device is reliable andvirtually fail-safe device and can raise an alarm when the relativehumidity rises above 62%, which is the deliquescent relative humidity ofsodium nitrite. Devices based on other salts will raise the alarm atother relative humidity levels above the deliquescent relativehumidities of the salts. For example, if sodium chloride is chosen, thealarm will go off when the relative humidity rises above the 75%deliquescent relative humidity of sodium chloride. The device can alsostore the history of the alarm situations and maintain a records totrack times and occurrences of excessive relative humidity in the air.

With regards to FIG. 1, an inter-digitated comb pattern 105, preferablymade of platinum, a very corrosion resistant metal, is printed on aquartz frit disk 110 whose pores contain sodium nitrite salt particles115. Quartz frit consists of fused quartz particles with interconnectedpores. Quartz frit is commercially available, generally, to filterliquids in chemistry laboratories. The salt particles cannot fall offthe disk because they are trapped in the interconnected pores in thefrit disc.

The quartz frit disk is soaked in sodium nitrite solution so that thesolution penetrates the pores in the quartz frit. The solution is thendried. The concentration of the solution may be saturated. Preferably,the solution is saturated with salt by adding more salt than thesolution can dissolve. For example, for a given salt, there is a fixedamount of salt the water can dissolve. Each salt has a solubility limit;i.e. sodium chloride has a solubility limit of 35 g in 100 ml of waterand sodium nitrite has a solubility limit of 81 g in 100 ml of water. Asan example, 90 gm of sodium nitrite is added to 100 mg of distilledwater. Of the nitrite added, 81 g will dissolve. The rest will settle tothe bottom of the beaker. The top liquid can be decanted to be used asthe salt solution to soak the quartz frit or the circuit board. Theundisclosed solid sodium nitrite may be discarded.

The comb patterns may be separated by about 0.5 mm spacing 120. The combpatterns may consist of platinum plating. Platinum is preferred becauseof its corrosion resistance to most salts and environments. Other metalswith similar properties such as gold or palladium may also be used.

Another implementation of the sensor may use the inter-digitated combpattern printed on other substrates besides the quartz frit disk such ason printed circuit boards that have been sand blasted to make the boardsurface rough enough to retain the salt particles bridging the combs.The pits on the printed circuit board between the combs may be loadedwith salt particles by drying the saturated salt solution applied to theboard. The circuit board surface may be roughened up for betteradherence to the salt solution. The inter-digitated comb pattern may bemade of other metals besides platinum or gold.

FIG. 2 depicts a sample implementation of the comb patterns in anelectrical circuit, with the comb pattern sensor printed on the samecircuit board as the electrical circuit that is used to monitor highrelative humidity events. A small constant voltage from power source 210of about 1 V is applied across the inter-digitated patterns while thecurrent flowing between the two comb electrodes is measuredcontinuously. The power source may be a battery. An operationalamplifier 230 will convert the current into voltage. The resistance R235 across the operational amplifier can be of the order of 1 MOhm.Under low relative humidity conditions, the conductivity between the twointer-digitated patterns is very low (resistance between the combelectrodes can be larger than 100 MOhm), and the measured current wouldbe less than 10 nA. The voltage from the circuit is monitoredcontinuously by a microcontroller 240 that would have a voltagethreshold programmed into it. Resistance and voltage levels aremonitored by microcontroller 240.

As the relative humidity increases, the sodium nitrite salt will remainrelatively dry, with high electrical resistance, until the air relativehumidity approaches 62%. Above 62% relative humidity, the salt willabsorb moisture and get wet and therefore become electricallyconductive; the microcontroller 240 will detect the rise of currentbetween the inter-digitated comb patterns. A rise of current from 10 nAto >1 mA is expected, as the relative humidity crosses the 62%threshold. If the leakage current goes above 1 mA, the microcontrollerwill cause alarm 250 to trigger and the data will be recorded in datalogger 245. The alarm indicates an incident of relative humidity in theair exceeding a predefined value.

If the relative humidity in the data center goes above 62%, the saltgets wet and electrically conductive. The flow of current between thecomb patterns above a threshold value, in this invention chosen to beabove 1 mA, will be the indication that the relative humidity in thedata center has gone above 62%. Once the relative humidity goes below62%, the salt will become dry and the current flow across the patternswill go below the threshold value. The leakage current time periodsabove and below the threshold value will be digitally logged in the datalogger 245 at regular time intervals and available for down loading to acomputer for display as a plot of high relative humidity events when therelative humidity went above 62% as a function of time.

The microcontroller can also control an air control unit 260 such as ahumidifier, dehumidifier, air conditioner or air dampener to affectcorresponding desired changes in the relative humidity levels in theair. An air mixer may be used to combine indoor and outdoor air toaffect changes in the indoor relative humidity.

The technique can be used to monitor a rise above another relativehumidity by choosing a salt with the appropriate deliquescent relativehumidity. Each salt has a deliquescent relative humidity above which itabsorbs enough moisture to get wet and therefore ionically conductive.For, example sodium nitrite has a deliquescent relative humidity of 62%at room temperature. If one wishes to monitor a rise above 75% relativehumidity, a quartz frit containing sodium chloride salt particles may beused due to sodium chloride having a deliquescent relative humidity of75%. Hence, a different salt solution may be used to test differentrelative humidity threshold levels. The salt solutions may be applied byvarious methods, such as either soaking the fritz disc or circuit toachieve maximum coverage or spraying the solution onto the combpatterns. Other methods of applying the solution may also be used.

Inter-digitated comb pattern may also be printed on other substratesbesides the quartz frit disk such as on printed circuit boards that havebeen sand blasted to make the board surface rough enough to retain thesalt particles bridging the combs. The pits on the printed circuit boardbetween the combs may be loaded with salt particles by drying thesaturated salt solution painted on the board surface. Theinter-digitated comb pattern may be made of other metals besidesplatinum or gold.

FIG. 3 demonstrates the relative humidity check process in a circuitimplementing an embodiment. The circuit determines that relativehumidity has exceeded the threshold level by measuring the leakagecurrent 300. If leakage current is not below 1 mA in 310, datacontaining relevant information such as date, time, and duration of thethreshold being exceeded is written to a data logger in 320. The alarmis triggered in 330. The circuit may be connected to an air control unit340 which can adjust relative humidity levels. In this example, the aircontrol unit is a humidifier, which is activated to reduce relativehumidity by 5%. The process then returns to step 300 for continuedmonitoring.

If the leakage current remains below the preset threshold of 1 mA instep 310, then relevant information such as date, time, and duration ofrelative humidity remaining below the threshold is recorded to the datalogger in 350. The process then returns to step 300 for continuedmonitoring.

FIG. 4 demonstrates an embodiment involving an air mixer that combinesindoor and outdoor air as another mechanism to control relative humiditylevels inside the server room. The current through the inter-digitatedcombs is measured for leakage in 410. If current leakage does not exceed1 mA, the process continues measuring for leakage in 420. If currentleakage exceeds 1 mA this indicates a high relative humidity level 430and action is taken to adjust the relative humidity level in the serverroom. Outdoor air 470 is mixed with indoor air 480 and combined with airmixer 490. Prior to reaching the air mixed, outdoor air may beconditioned by throttling the amount of air and/or dehumidifying theoutdoor air to achieve desired relative humidity levels.

In another embodiment, relative humidity forecasting from nationalweather models may be used to make predictions concerning futurerelative humidity conditions, allowing proactive measures to be taken.Such measures may include closing air dampers, and/or adjustingtemperature based on predicted changes in air and relative humiditylevels. The sensors can then be used to monitor the effectiveness andaccuracy of such measures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise” (andany form of comprise, such as “comprises” and “comprising”), “have” (andany form of have, such as “has” and “having”), “include” (and any formof include, such as “includes” and “including”), and “contain” (and anyform contain, such as “contains” and “containing”) are open-endedlinking verbs. As a result, a method or device that “comprises”, “has”,“includes” or “contains” one or more steps or elements possesses thoseone or more steps or elements, but is not limited to possessing onlythose one or more steps or elements. Likewise, a step of a method or anelement of a device that “comprises”, “has”, “includes” or “contains”one or more features possesses those one or more features, but is notlimited to possessing only those one or more features. Furthermore, adevice or structure that is configured in a certain way is configured inat least that way, but may also be configured in ways that are notlisted.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiment was chosen and described in order to explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention throughvarious embodiments and the various modifications thereto which aredependent on the particular use contemplated.

We claim:
 1. A method to monitor the relative humidity of the airexceeding a predefined value, the method comprising: providing metallicinter-digitated comb patterns printed on a medium having spacing inbetween the patterns; coating the patterns and medium with a liquidsolution containing salt, the salt having a deliquescent relativehumidity; allowing the solution to dry; connecting, in series, a powersupply, a high resistance resistor and a microprocessor to the combpattern thereby creating an electrical circuit; connecting at least oneof a data logger and an alarm circuit to the microprocessor; monitoring,by the microprocessor, the resistance of the circuit as voltage passesthrough the circuit; and triggering the alarm circuit in response to thevoltage exceeding a threshold value.
 2. The method of claim 1 whereinthe medium is a printed quartz frit disk.
 3. The method of claim 1further comprising writing data to the data logger.
 4. The method ofclaim 1 further comprising activating an air mixer controlled by themicroprocessor to combine indoor and outdoor air to regulate relativehumidity levels of the indoor air.
 5. The method of claim 1 furthercomprising activating an air control unit controlled by themicroprocessor to regulate relative humidity levels of the indoor air.6. The method of claim 1 wherein the comb patterns are made of corrosionresistant metal.